Created attachment 666308[details]
PNG showing problem with content not redrawn when reverse scrolling
Since DLBI landed scrolling over top stories grid on The Verge's homepage then scrolling back to reveal them again shows regions where content has not been redrawn.
See attachments for a picture of the problem, and how the page should look.
This was observed with the moz-central win32 PGO build built from the following change-set:
http://hg.mozilla.org/mozilla-central/rev/a680fd777c3b